A coolant cooler dissipates excess heat produced by an internal combustion engine of a motor vehicle to ambient air. Moreover, with supercharged internal combustion engines, a charge-air cooler cools air, which has been heated and compressed in a supercharger, and dissipates heat to ambient air. The operations of cooling charge air and coolant are fundamentally different. The coolant undergoes only a small drop in temperature because the coolant has a high heat capacity. A large heat quantity thus can be exchanged even with slight cooling. In contrast, the charge air temperature is considerably higher when it enters the charge-air cooler and has to be considerably lower than that of the coolant as the charge air exits.
Charge-air coolers can be air cooled or liquid cooled. In liquid-cooled charge-air coolers, more straightforward charge-air guidance is usually possible, and the overall volume of these charge-air coolers can be smaller than the air-cooled design. If the engine coolant cools the charge air, the charge air can only be cooled approximately to the coolant temperature. If a lower charge-air temperature is sought, it can only be achieved by an additional coolant circuit that is capable of producing a lower outlet temperature or, more straightforwardly, by air-cooled charge-air coolers. The air-cooled design is widely used in passenger cars and commercial vehicles. The charge-air coolers are thus generally air-cooled charge-air coolers.
It is known from the publication ATZ Automobiltechnische Zeitschrift (Automotive Journal) (1981), No. 9, pages 449, 450, 453; to arrange the charge-air coolers upstream of the coolant cooler and have part of the end surface of the coolant cooler overlap the charge-air cooler on the air side. The reason for this arrangement is that, in the case of the charge-air cooler, a lower target temperature has to be reached than in the case of the coolant cooler. The lower target temperature is ensured by cooling with fresh air flowing against the same. This conventional arrangement is disadvantageous in that cooling air flowing on the air side becomes heated to a very pronounced extent in the upstream charge-air cooler. Because the heated air reaches the downstream coolant cooler, it can only slightly cool the coolant in the overlapping coolant-cooler part. The coolant cooler of such an arrangement thus requires a relatively large surface area to achieve the necessary cooling capacity. Moreover, very large cooling-air streams are necessary, and they require in some cases very high fan capacities.
European Patent Application EP 522 288 discloses a heat exchanger arrangement that has a coolant cooler and a charge-air cooler. The charge-air cooler is of split design and, in relation to a cooling air stream, has one charge-air-cooler part located upstream of the coolant cooler and one charge-air-cooler part located downstream thereof. This arrangement makes it possible for at least one part surface of both of the charge-air cooler and of the coolant cooler to be exposed to fresh air. Such an arrangement has a disadvantage in that, on account of the charge-air cooler being split into two charge-air-cooler parts, increased design outlay is necessary, in particular in terms of the charge-air-side connection of the two charge-air-cooler parts to one another for passing on the charger from one charge-air-cooler part to the other. Because this operation involves the charge air being passed on, there is an additional pressure drop in the charge air. Furthermore, there is an increase in the installation space, in particular the installation depth in the air-flow direction within the motor vehicle in comparison with a conventional arrangement, since three heat-exchanger planes, namely the first part of the charge-air cooler, the coolant cooler, and the second part of the charge-air cooler, are arranged one behind the other on the air side.
European Patent Application EP 522 471 discloses a heat exchanger arrangement that has a coolant cooler and a charge-air cooler. Both the coolant cooler and the charge-air cooler are of split design. This arrangement likewise is disadvantageous in that increased design outlay is necessary for passing on the charge air and the coolant to the respectively associated charge-air-cooler part and coolant-cooler part.
The present invention relates to a heat exchanger arrangement that can reduce the design outlay. Furthermore, the installation space, both in terms of the depth in the air-flow direction and perpendicularly thereto, can be kept as low as possible, to achieve the greatest possible heat-exchanging capacity over a smallest possible surface area.
A heat exchanger arrangement according to the present invention can comprise a coolant cooler and a charge-air cooler. Both the coolant cooler and the charge-air cooler are exposed to ambient air. The coolant cooler comprises a plurality of tubes through which coolant to be cooled flows and heat dissipating ribs connected to the tubes. The charge-air cooler similarly comprises a plurality of tubes through which hot charge air to be cooled flows and heat dissipating ribs connected to the tubes. The charge-air cooler has a charge-air inlet region from which hot charge air is introduced into the charge-air cooler and a charge-air outlet region from which cooled charge air exits.
According the present invention, the charge-air cooler is positioned downstream of the coolant cooler relative to the direction of cooling air flow. The charge-air cooler has an overlapping region in which the coolant cooler and the charge-air cooler overlap one another and a non-overlapping region in which a portion of the charge-air cooler projects substantially perpendicularly to the cooling air flow direction, beyond the coolant cooler. The non-overlapping region is formed at least in the charge-air outlet region and is cooled directly by ambient cooling air, whereas the overlapping region is cooled by the ambient cooling air that cools the coolant cooler.
The surface area of the charge-air cooler can be smaller or substantially the same, or larger than that of the coolant cooler. The charge-air cooler and the coolant cooler can be offset with respect to one another perpendicularly to the air-flow direction.
The density of the ribs of the charge-air cooler can be greater in the non-overlapping region than in the overlapping region. The density of the ribs and/or the mutual spacing of the ribs on the outer surface and/or the interior of the charge-air cooler can be varied. The spacing between the tubes of the charge-air cooler can be smaller in the non-overlapping region than in the overlapping region. The charge-air cooler can have a multiple rows of tubes, with a greater number of tube rows in the non-overlapping region than in the overlapping region. The non-overlapping region of the charge-air cooler can also have a greater depth in the air-flow direction than the overlapping region.
According to another aspect of the invention, at least one additional heat exchanger is arranged upstream of and at least partially overlaps the non-overlapping region of the charge-air cooler. The additional heat exchanger can be connected downstream of the charge-air outlet region to further cool the charge air. The additional heat exchanger can also be integrated with at least one of the charge-air exchanger and coolant cooler and the additional heat exchanger can be arranged upstream, downstream or alongside thereof.
The additional heat exchanger is adapted to be connected to a coolant circuit that is separate from the charge-air cooler and the coolant cooler, such as an exhaust-gas cooling circuit, or that is part of the charge-air or coolant cooling circuit. Thus, the additional heat exchanger can be an exhaust-gas heat exchanger.